Assistant general manager Ricky Bennett said right-hander Danny Meszaros (Triple-A Round Rock), catcher Jonathon Fixler (Double-A Corpus Christi) and shortstop Marcos Cabral (Corpus Christi) have been suspended.
Earlier Wednesday, Major League Baseball announced pitcher Richard Rodriguez of the Astros' Dominican Summer League team had been suspended.
Meszaros, who advanced to Triple-A after being drafted in the 48th round in 2008, was 2-1 with a 5.40 ERA in seven games at Round Rock after going 3-1 with a 3.09 ERA in 26 games at Double-A Corpus Christi to start the year. Fixler was hitting a combined .242 with six homers and 22 RBIs between Corpus Christi and Class A Lexington, and Cabral was hitting .259 with five homers and 24 RBIs between Round Rock and Corpus Christi.
"The Houston Astros fully support the efforts of the Commissioner's Office to rid our sport of any type of inappropriate drug use," Astros general manager Ed Wade said in a statement. "Our players and staff have been briefed, counseled, educated and warned about what the ramifications and consequences are when they choose, either knowingly or not, to violate the MLB drug policy. And yet, despite the best efforts of MLB and the Astros, we still have individuals who abuse our game by ignoring reality. We are embarrassed by these types of suspensions. They are a smear on our game and our organization, and we will redouble our efforts to make sure the message gets through."